A memory card with a memory chip built therein has been used in these years as one of recording media for storing information. Since the memory card is excellent in portability, it has been widely used as a recording medium of portable electronic devices such as a portable information terminal or a cell phone.
These portable electronic devices have been downsized and reduced their thicknesses in order to improve the portability. This market trend requires the memory card to be downsized and have a thinner body. On top of that, the memory card is specified its shape, size, and thickness by the trade standard, so that the memory card must meet this standard before it achieves a greater capacity.
On a memory chip mounted on a lead frame, another memory chip is layered but shifted from the previous one. The electrodes of these two memory chips and an electrode of a control chip mounted on the lead frame are coupled to the lead frame via a gold wire, so that the thickness of the memory card can be reduced. This technique is disclosed in, e.g. patent document 1.
However, the memory card disclosed in patent document 1 is limited to decrease its thickness because the memory chips are layered together. This structure also complicates the memory card in construction. The memory chips and the control chip are mounted onto the lead frame by a wire bonding method, so that the chips, wires, and lead frame need to be sealed with thermosetting resin after they are mounted. At this time, a sealing layer is to be thick enough for covering the memory chips and the wires, so that the memory card is limited to be downsized or to be thinner. Since a sealing step is needed in addition to the mounting step, a reduction in the manufacturing cost is limited.
A flip-chip mounting method is available as one of the methods of mounting semiconductor chips, such as a memory chip and a control chip, onto a circuit board. This method bonds an electrode of a semiconductor chip to an electrode of a circuit board with a bump therebetween. According to the flip-chip mounting method, a semiconductor chip is urged against a circuit board via resin applied to an electrode of the circuit board, and the resin is hardened in this state for mounting the semiconductor chip to the circuit board. This method allows eliminating a sealing layer supposed to cover the semiconductor chip mounted on the circuit board, so that the memory card can be smaller and thinner than the memory card disclosed in patent document 1. In this case, a memory chip and a control chip are not layered together on the circuit board, but they are preferably placed flat on the circuit board in order to reduce the thickness of the memory card. These semiconductor chips are preferably placed as close as possible to each other in order to downsize the memory card.
However, the foregoing flip-chip mounting method has the following problems: When a semiconductor chip is urged against a circuit board, the resin beneath the semiconductor chip spreads over the surrounding of the chip, and hardens in this state. When a plurality of semiconductor chips are placed as close as not greater than 1 mm to each other, the resin to be used for mounting one semiconductor chip spreads over the area supposed to be used for mounting the other semiconductor chips, and hardens there. A resin layer applied to an area where another chip is supposedly mounted changes in quality because the resin of one semiconductor chip is hardened. As a result, it is difficult to mount this another semiconductor chip to the supposed area. To overcome the spread of the resin layer or the change in quality, if the semiconductor chips are placed with a space over 1 mm between each one of the semiconductor chips, the memory card will not be downsized. As discussed above, it is difficult to mount the semiconductor chips as close as possible, e.g. not greater than 1 mm between each semiconductor chip, so that the memory card is limited to be smaller. Patent Document 1: Unexamined Japanese Patent Publication No. 2004-13738